A volcano named Tvashtar is near Io's North Pole. Two different spacecraft have "seen" Tvashtar erupting. The Galileo spacecraft spotted a huge lava lake in the volcano's crater. It also took pictures of an eruption of a huge lava "curtain" that was 25 km (16 miles) long and at least a kilometer (three thousand feet) high! The New Horizons spacecraft took pictures of an eruption from Tvashtar in 2007.

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